Boswell: But, Sir is it not somewhat singular that you should happen to have Cocker's Arithmetic about you on your journey? Dr. Johnson: Why, Sir if you are to have but one book with you upon a journey, let it be a book of science. When you read through a book of entertainment, you know it, and it can do no more for you; but a book of science is inexhaustible.

The Journal of a Tour to the Hebrides: With Samuel Johnson, LL.D. By James Boswell,... (ed. 1785)